This so-called "Purex Process" of solvent extraction for uranium is well known in the nuclear fuel art and industry. For example, the process is described in the U.S. Pat. No. 3,357,802, issued Dec. 12, 1967, U.S. Pat. No. 4,595,529, issued Jun. 17, 1986, U.S. Pat. No. 4,758,313, issued Jul. 19, 1988, and discussed in extensive detail in Chapter 10, entitled "Fuel Processing," namely pages 457 to 514, of Nuclear Chemical Engineering, by Benedict et al, McGraw-Hill Book Company, 1981. The disclosed contents of the fore going cited patents and section of the text are accordingly incorporated herein by reference.
Briefly, the Purex Process consists of a sequence of chemical steps or operations comprising initially treating the waste of scrap material or spent fuel containing uranium compounds with an aqueous solution of nitric acid (HNO.sub.3), and thereby dissolving the uranium to produce uranyl nitrate (UO.sub.2 (NO.sub.3).sub.2) and other acid soluble components within an aqueous phase. This aqueous phase containing the acid dissolved components including uranyl nitrate, and any acid insoluble components of the waste is passed down through an extraction column while an organic phase of tri-butyl phosphate in an organic diluent of a paraffinic mixture such as kerosene is passed up through the extraction column in counter-current flow with the aqueous phase. The soluble uranium compounds comprising uranyl nitrate of the aqueous phase are extracted therefrom by the organic phase and combined with the tri-butyl phosphate. This separates the uranium and carries it within the organic phase from the extraction column. The aqueous phase, and the organic phase each exit from the extraction column at opposite ends from each other and from their respective entries, the aqueous phase with the acid soluble raffinate contaminants and the organic phase with the separated uranium.
The organic phase effluent from the extraction column carrying the separated uranium compounds is then passed up through a stripping column while water is passed down through the stripping column in counter-current flow with the organic phase. The water releases the uranium from the tri-butyl phosphate of the organic phase whereby it is transferred to and carried within the aqueous phase. The aqueous phase, and the organic phase each exit from the stripping column at opposite ends from each other and from their respective entries, the aqueous phase containing the uranium compounds for recovery separated from contaminants. The organic phase is then recycled back through the extraction column. Typically, the procedure is carried out with a continuous flow of all components through the system comprising the extraction column and stripping column.
The columns are typically agitated by either pulse pumps or reciprocating plates to permit optimal droplet formation and coalescence on each plate. The agitation is most commonly referred to as mixing energy. Excessive mixing energy or flow rates can cause flooding, a condition which precludes flow of one or both liquid operating mode phases in the column due mainly to coalescence of small droplets into larger droplets. Mixing energy is critical to efficiency of the extraction column and helps establish a characteristic uranium profile.